curl --request POST \
  --url https://sending.sendrapp.org/email \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "recipients": [
    {
      "email": "jsmith@example.com",
      "name": "<string>",
      "substitutions": {}
    }
  ],
  "emailConfig": {
    "subject": "<string>",
    "from": "jsmith@example.com",
    "fromName": "<string>",
    "body": "<string>",
    "headers": {
      "X-Tenant": "<string>"
    }
  }
}
'

{
  "message": "<string>",
  "limits": {
    "limit": 123,
    "used": 123,
    "remaining": 123,
    "requested": 123
  }
}